This invention relates generally to cyclical timers for electrical devices and in particular to a thermal timer, a thermal control system, a circuit for operating an electrical device, and a thermal actuator for a thermal timer.
In the past, various and sundry cyclical timers have been utilized to control the energization of many different types of electrical devices. Some of the well known past cyclical timers were operated by motor driven cams, and other such past cyclical timers were switch operated. Of course, a motor, either electric or spring driven, was commonly utilized to drive some of these past cyclical timers. In other past cyclical timers, a bimetal element was cyclically heated and cooled to actuate a switch for controlling a circuit for an electrical device.
One of the disadvantageous or undesirable features of some of the past cyclical timers is believed to be that it was difficult to predeterminately attain desired on-off periods or timers of generally equal duration. Another disadvantageous or undesirable feature of some of the past cyclical timers is believed to be that it was difficult to attain timing characteristics in which both the on-off periods or times are extremely short. Another disadvantageous or undesirable feature of some of the past cyclical timers is believed to be that they had to be calibrated or adjusted to compensate for ambient temperature. Still another disadvantageous or undesirable feature of some of the past cyclical timers is believed to be that they did not readily dissipate heat and were therefore rather slow acting. And yet another disadvantageous or undesirable feature of some of the past cyclical timers is believed to be that it was necessary to drive them with a motor thereby to increase the complexity and cost of those past cyclical timers.